The Problem of Trachoma within an Onchocerciasis-Endemic Zone in Kaduna: Need for a Multilateral Approach?

Onchocerciasis as a risk factor for night blindness

PURPOSE

In the Kaduna State Nigeria Onchocerciasis focus, the prevalence of reported night blindness (RNB) was 12.9%, higher than the national average (1%), and a control non-onchocercal community (0.83%, P < 0.0001). Risk factors for RNB were explored.

METHODS

This was an analysis of baseline data from the phase three ivermectin trials in Kaduna (1988-1995). 6831 subjects in the onchocercal zone and 1563 in the control zone were examined. Ordinal logistic regression was used to assess the relationship between microfilaria load (uninfected, low (<10 mf/mg), moderate (10-49 mf/mg) and high (50+ mf/mg)) and likelihood of RNB.

RESULTS

Ocular evidence of vitamin A deficiency (Bitot spots or xerophthalmia) was absent in both populations. The excess risk of nightblindness attributable to domicile in this onchocerciasis-endemic area was 11.9% with a population attributable fraction of 92.2%. The prevalence of RNB and age-adjusted odds ratio increased with higher microfilaria load (P < 0.0027.) Subjects with onchocerciasis-related ocular lesions such as optic nerve disease (OND; age-adjusted OR 2.29, 95% confidence interval, CI, 1.86-2.83), sclerosing keratitis (OR 2.75, 95% CI 2.10-3.50), and onchocercal chorioretinitis (OR 1.66, 95% CI 1.22-2.26) were significantly more likely to report night blindness. Overall, subjects with a primary diagnosis of 'ocular onchocerciasis' were 50% more likely to report night blindness. OND, cataract and trachoma together accounted for 52% of all RNB but OND (onchocerciasis-related in 80% of cases) emerged as the single most common associated pathology in 30% of cases.

CONCLUSIONS

Onchocercal infection probably accounted for the excess of RNB in this focus.

Trachoma surveys 2000-2005: results, recent advances in methodology, and factors affecting the determination of prevalence

With the advent of VISION 2020 and GET 2020 inaugurated by the World Health Organization, it is timely to provide an update of the methodology employed in trachoma surveys, given that a significant number of individuals in many undeveloped and developing countries still suffer from this ophthalmic disease. The advent of Trachoma Rapid Assessment and Asymmetrical Sampling Rapid Trachoma Assessment has enabled faster identification of trachoma-endemic areas, though population-based surveys are still required prior to intervention. Research into factors affecting prevalence determination has shown that mobility, clustering, and seasonality should all be taken into account regarding survey design. In addition, recent advances in laboratory testing have given us new insight into trachoma infection patterns and a better understanding of the disease course. In this review, we examine advances in survey methodology and the results of trachoma surveys since 1999, and other issues relevant to the determination of trachoma prevalence. Based on recent findings, we recommend that pooled nucleic acid amplification testing be used to augment clinical assessment in areas where trachoma prevalence is greater than 20%. Further, we suggest that trachoma follicular and trachoma follicular or trachoma intense, as markers of the disease, be reported separately.